Electromagnetic friction device



Dec. s, 193s.

A. B. CADMAN ELECTROMAGNETIC FRICTION DEVICE Original Filed July 6, 1936 2 Sheets-Sheet l NVENTOL/ Cadwan Dec. 6, 1938. A. B. cADMAN j v ELEGTROMAGNETI FRICTION DEVICE original Filed July e, 193e 2 sheets-sheen 2 NVENTOQ. dd @Cady/an fw, wm, aw

Patented Dec. 6, 19838 UNITED STATES PATENT OFFICE Application July 6, 1936,r Serial No. 89,094

Renewed February 28, 1938 16 Claims.

This invention relates to electromagnetic friction devices for brakes and clutches, and more particularly to those in which a frictional force is derived by electromagnetic attraction between a substantially flat annular armature ring and the concentric pole faces of a second ring carry-` ing an electromagnetic winding.

The general object of the invention is to provide, in an electromagnetic friction device of the above character, a novel armature construction which is simple and inexpensive to' manufacture, which eliminates the detrimental effect of residual magnetism, which enables the friction device to operate at maximum eiciency without the necessity of prolonged service use or wearing in of the parts, and which is not subject to objectionable distortion by the heat to which the armature is subjected in service.

The invention also resides in the novel con- 20 struction of the amature by which manufacture is facilitated and a high degree of exibility obtained in the construction of the armature as a. unit.'

Other objects and advantages of the invention will become apparent from the following detailed description taken in connection with the accompanying drawings, in which' Figure l is a diametrcalsectional view of an electric brake equipped with a friction device embodying the features of the present invention.

Fig..2 is a face view of thearmature unit constructed in accordance with the present invention.

Fig. 3 is a fragmentary sectional view. taken substantially along the line 3-3 of Fig. 1.

Fig. 4 is a fragmentary perspective view looking toward the rear of the armature ring.

Fig. 5 is a fragmentary rear elevational view of the armature ring and its mounting.

Fig. 6 is a fragmentary cross sectional view taken along the line 6 6 of Fig. 5.

- While the invention is susceptible ofjvarious modifications and alternative constructions,I I have shown in the drawings .and will herein describe in detail the preferred embodiment,l but it is to be understood that I vdo not thereby intend to limit the invention to the specific form disclosed, but intend to cover lall modifications and alternative constructions falling within the spirit and scope of the invention as expressedin the appended claims.

In the'A drawings; the invention is embodied in anelectrlc brake fora vehicle wheel 6 including 'a rotatable drum 1 having'the-usualkflange 8 bolted or otherwise secured tothe wheel hubn9., 'I'he inwardly opening end of the drum is closed by an annular plate I suitably secured to a nonrotatable support (not shown). The non-rotatable friction element of the brake is of the band type comprising a metal strip II encircling inwardly projecting flange I2 on the anchor plate and carrying segments I3 of friction material. Fittings I4 are secured to the opposite ends of the strip II and drawn by a. spring I5 into abutting engagement with the opposite end surfaces of a stop I6 rigid with the anchor plate.

'I'he electromagnetic operator in which the present invention is embodied is utilized to spread the ends of the band apart and thereby set the brake. It comprises two rings Il and' I8 of magnetic material arranged concentric with the drum l and adapted. for axial gripping engagement. The ring Il, which will be described in detail later, constitutes the magnetic alrmature'and is floatl ingly supported from the drum so as to rotate therewith and at the same time is adapted for some degree of axial movement. To this end, the backA of the ring is secured at annularly spaced points to the ends of flexible metal strips I 9 which extend in a substantially tangential direction and are spot welded at their other ends with a ring ,20 in turn riveted to the drum flange 8. The strips I9 areftensioned to urge the armature ring I'I awayfrom the drum flange and thereby mainytain the face of the ring in constant light me chanical contact with the face of the magnet I8. The strips act in tension to prevent relative rotation between the rings I1 and 20 in one dir'ection. Relative rotation in the other direction is prevented by engagement between lugs 2I rigid with the armature ring land flanges 22 rigid with the ring 20. l

The ring I8 constitutes a magnetic core and is U-shaped in cross section with a winding 23 disposed between and enclosed by its two concentric poles 24 and adapted to be energized from a storage battery orr other source of 'electrical power. Plates 25` of non-magnetic material are rmounted betweeny the poles and provide va wear resisting surface substantially iviush with the end faces ofthe poles and adaptedl to sustain the axial pressure lbetweenthe two magnetic rings. The magnet ring is supported for oscillation about the drum axis by'a circularfiange portion 28 of the anchor plate. Y ,v

Projecting rigidly from theouter magnet pole are two actuating lugs 21 having oppositely facing surfaces positioned to abut against lugs 28 which `are rigid with the ttings I4 on the brake bend.

Upon movement of the magnet in either direction away from normal brake-released position (Fig. 3), one or the other of the lugs 21 will move its end of the brake away from the stop I6, thereby expanding the band and pressing its entire friction surface against .the drum.

Such actuation of the band takes place whenever the winding 23 is energized with the wheel in motion. This produces a magnetic ux of high intensity in the closed magnetic circuit which encircles the winding through the opposite sections of the magnet core and armature. The resulting magnetic attraction causes gripping engagement between the friction surfaces of the two rings proportional to the strength of the energizing current, whereupon the magnet ring will be driven frictionally by the armature ring thereby moving with the wheel a short angular distance. In this circumferential movement, one end of the band is moved away from the stop I6 expanding the band and thereby pressingthe segments I3 against the drum surface. After the normal clearance has been taken up, angular movement of the magnet ceases, causing slippage between the ring surfaces in the continued rotation of the wheel. When the current flow is interrupted, the spring I5, acting through the medium of the fitting I4 and the lug 21 serves to restore the magnet as well as the actuated end of the band to normal brake-released position.

Inasmuch as the friction faces of the rings I1 and I8 are constantly urged into light mechanical contact by the springs I9 while the winding 23 is deenergized, it is unncessary for the magnetic flux produced by the initial energization of the winding to* overcome an air gap of any substantial width between the rings. As a result, the attractive force and, therefore, the degree of braking action is directly proportional to the strength ofthe energizing current.

Owing to the extremely low reluctance of the magnetic ux circuit which encircles each circumferential section of the winding 23, a magnet 0f the above character is capable of exerting a powerful attractive force which is an invariable function of the energizing current provided, however, that the coacting faces of the armature ring I1 and the poles 2l are in full contact. Unevenness of the armature surface or distortion thereof under the heat developed in service use will seriously impair the eiliciency of the magnet as well as the controllability of the friction device as a whole.

The present invention contemplates a construction of the armature ring in which the tendency of the armature face to distort upon being heated is reduced to a minimum and which permits the active face of the ring to be formed with a high degree of flatness without adding to the manufacturing cost. To these ends, the armature ring is formed of relatively short segments 30 arranged circumferentially in end-to-end relation and flexibly'connected together and supported in a manner such as to obtain a, high degree of relative flexibility not only'between the segments but of the parts of the individual segments and the parts by which the segments are interconnected. In order to obtain maximum stability inthe fiatness of the armature face in actual service use, I have discovered that a relatively large number of segments should be employed. Preferably, approximately eighteen segments are used but as used herein the terms relatively large number contemplates more than twelve segments.

i. For a purpose to appear later, each segment is composed of rigidly connected outer and inner portions 3|)a and 30h. To increase the relative flexibility between the segments, the segments are joined together by two concentric rings 3| and 32 of fiat sheet metal lying against the backs of thelsegments and rigidly connected to the individual segments at single points of attachment. Preferably, these points are located midway between the edges of the rings and segment portionsand between the radial edges of the latter, being formed by spot welds 33. With this form and location of the attachment means, an effective connection between the parts is formed without the possibility of causing uneven distortion of the connected parts. Since the welds are 1ocated along the radial center lines of the segments, the parts of the latter are free to flex relative to these lines thereby minimizing the distortion which has been found to be most detrimental in friction devices of the present character.

It has been found that the relative radial widths of the rings appreciably aiect the ability of the armature to withstand heating without distortion of its active face, it being desirable to employ an inner ring ofsomewhat greater radial width than the outer ring. As shown herein, the rings are of such relative widths that their respective face areas are substantially equal.

To provide a connection between the ends'of the springs and the back of the armature ring, which connection will withstand the torque to which the springs I9 are subjected and will. at the same time permit freedom of relative flexing of the segments 30, the ends of the springs are secur-ed as by welding to the ends of brackets `35 in the form of elongated metal strips extending substantially tangentially of the armature ring. The other end of each bracket is secured to the carrying ring 3| at a single point of attachment.

For this purpose, a hole 36 (Fig. 6) is punched 'through the ring 3| to receive a punched out projection 31 of the bracket which, when the parts are assembled, projects into contact with the back of one segment 30. By applying a welding electrode in the depression 38, the bracket 35, the ring 3|, and the segment 30 become rmly welded together at a single point. The portion of the ring 3| surrounding the projection 31 is enlarged as indicated at 39 (Fig. 5) so as to provide sumcient area for the welds 4| by which the opposite segment 30 may be attachedto the enlarged portion of the ring 3|. To prevent bending of the brackets 35 under the torque encountered during application of the brake, the end of each bracket opposite the weld is formed with a lateral projection 42 spaced circumferentially from the weld and-bearing against the back surface of the ring 3 By constructing the armature ring as above described of segments of relatively short circumferential length, by attaching these segments at single points near their center lines to the separatecarrying rings 3| and 32 and by attaching the springs I9 to one of the rings at a single point, a high degree of fiexure between any spaced points on the face of the amature is permitted with the result that the parts are free to expand disposed in a common plane. Through the use of 75 armaturerings of this construction, it lhas been AV.found,that the maximum eiciency of the magneticdriction device may be obtained at the outset without the necessity of wearing in the parts or of prolonged service use.

To eliminate the detrimental effect of residual magnetism in maintaining the friction faces in gripping engagement after the magnetis deenergized, a non-magnetic gap 45 on the order of a few thousandths of an inch in width is interposed in the magnetic circuit. For this purpose, each segment 30 is formed as above described in two parts 30 and 3&1h separated by a thin ribbon 43 of non-magnetic material such, for example, as brass.

To secure the inner and outer parts ofthe segments together and provide a non-magnetic gap of uniform width without the necessity of heating the parts to a distorting temperature, the present invention contemplates the formation by arc welding of one or more beads 44 of non-magnetic material such as bronze along the backs of the segment parts 30a and 30b and overlapping the adjacent edges of the latter. electric arc welding to form the bead, a minimum amount 'of heat is required for welding, this being highly localized so that there is little danger of the active face of the segments becoming di'storted. Since the welding heat is applied only to-the backs of the segments, there is no possibility of scale being formed on the friction face so that no subsequent treatment of this face is required. Moreover, the parts of the segments may easily be held in the desired position while the bead is being formed with the result that a non-magnetic gap of uniform width is obtained.

I claim as my invention:

1. lAn electromagnetic friction device having a magnet and an armature therefor with cooperating iiat annular faces, said armature comprising a plurality of segments arranged circumferentially in end-to-end relation, a flat ring rigidly attached to the back of each segment and having an enlarged portion with a hole therethrough opposite one of said segments, a bracket through the medium of which said armature is supported for axial movement, said bracket lying against said ring land having a projection extending through said hole and a weld formed on said projection rigidly uniting said bracket, said ring and said last mentioned segment at a single point'of attachment whereby to permit independentfiexure of said segment and said ring relative to said bracket.

2. An electromagnetic friction device having a magnet with concentric annular pole faces disposed in a common plane, an armature ring overlapping said pole faces and comprising a plurality of independently'movable segments arranged circumferentially in end-to-end relation and a ring lying against the backs of said segments and rigidly attached to the individual segments whereby to permit relative flexing between the segments, a plurality of flat bars extending in tangential directions and'lying against said ring at annularly spaced pointsI therearound, one end of each of said lbars being rigidly secured to said ring at a single point of attachment whereby to permit independent ilexure of the ring relative to said bars, and means including a second ring rotatably supporting said amature from the other ends of said bars, said last mentioned ends having bearing engagement with said second ring.

3. An electromagnetic friction device having a magnet with concentric annular pole faces dis- By employing posed in a common plane, Aan armature ring overlapping said faces and comprising-a plurality of independently` vmovable lsegments arranged circumferentially in end-to-end relation anda ring lying against the backs of said segments and rigidly attached to the individual segments whereby to 'permit relative flexing betweenthe segments,

a plurality of annularly spaced brackets each welded to said ring at a single point of attachment whereby to permit independent flexure of said brackets and said ring, and means rotatably u supporting said armature through'the medium of said brackets. I

4. An `electromagnetic friction device having a magnet and an armature therefor with cooperating annular, faces, said armature comprising a plurality of ring segments arranged circumferentially in end-to-end relation and two thin metal rings concentrically arranged and disposed in a common plane, said rings being welded to the inner and outer portions of said segments at single points of attachment intermediate the ends of said segments andthe sides of said rings.

5. An electromagnetic friction device having a magnet and an armature therefor with cooperating annular faces, said armature comprising a plurality of ring segments arranged circumferentially in end-to-end relation, a plurality of flat metal'rings concentrically arranged and disposed in a common plane, and means rigidly, connecting each of said rings and each of saidsegments at single points lof attachment located midway between the radial sideedges of said segments and midway between the sides of said rings.

6. An electromagnetic friction device vhaving `a magnet and an armature therefor with cooperating annular faces, said armature comprising a, plurality ofring segments arranged circumferentially in end-to-'end relation and two thin metal rings vconcentrically arranged and disposed in a common plane, and means rigidly joining each ring and the inner and outer portions of said segments at single points of attachment intermediate the ends of said segments and the sides of said rings, said inner ring being of greater radial width than said outer ring.

-7. An electromagnetic friction device having a magnet and an armature therefor with cooperating annular faces, said armature comprising a plurality of ring segments arranged circumferentially in end-to-end relation and two thin metal rings concentrically arranged and lying against the backs of said segments and welds rigidly joining each of said rings and segments while permitting independent fiexure of each segment and relative fiexure between the segments.

8. An electromagnetic device having a magnet and an armature therefor with cooperating annular faces, saidarmature comprising a multiplicity of relatively movable independent segments and a relatively flexible ring secured to the back of each segment at a single point of attachment intermediate the edges of said ring and the four edges of said segments. v

9. An electromagnetic device lhaving a magnet and an armature therefor with cooperating annular faces, said armature comprising a multiplicityA with'cooperating annular faces, saidarmature 75 ring comprising a relatively large number of independently movable segments.

11. An electromagnetic device having a. magnet and a unitary armature ring therefor with cooperating annular faces, said armature ring comprising a relatively large number of segments independently movable relative to each other and each arranged for flexure relative to a single point of support.

12. An electromagnetic friction device having a magnet and an armature therefor with cooperating annular faces, said armature comprising aV eachl segment and rigidly connecting the adjacent edges of said portions.

14. An electromagnetic friction device having a magnet and an armature therefor with cooperating at annular faces, said armature comprising a plurality of ring segments arranged in endtQ-end relation and each divided into inner and outer concentric portions separated by a nonmagnetic gap of narrow radial width, and nonmagnetic metal electrically welded to the back of each segment and overlapping the adjacent edges thereof whereby to rigidly unite the portions of each segment.

15. An electromagnetic friction device having a magnet and an. armature therefor with cooperatlng annular faces, said armature comprising a plurality of segments arranged Acircumferentially in end-to-end relation, a strip of metal lying against the backs of said segments and supporting the same to permit of relative flexing between the individual segments, said strip having a hole therein opposite'one of said segments, supporting means for said strip including a plate lying against the strip and having an integral projection extending through said hole, anda weld uniting said projection and said one segment whereby to provide a single point of support for the latter. f

16. An electromagnetic friction device comprising a magnet having spaced pole faces and an armature adapted to overlap said faces, said armature comprising a relatively large number of plates of magnetic material arranged adjacent each other in end-to-end relation, and means attached to the individual plates at points spaced intermediate the edges thereof and rigidly joining the adjacent plates into a unitary assembly whereby to permit flexure of all parts of each' plate relative to the point of support of the plate.

ADDI BENJAMIN CADMAN. 

